Containers having exterior closure attachment means formed adjacent extended neck portions are relatively abundant in the industry. Although not as common as external attachment means, internal attachment means may also be found on some thermoplastic containers. Several methods of molding thermoplastic containers having such internal attachment means are available in the art. U.S. Pat. No. 4,115,496, which issued to Thomas J. Krall on Sept. 18, 1978, for example, discloses a method for molding a threaded bunghole in a blow-molded article. The particular method described comprises the steps of: (a) positioning a parison between open mold sections; (b) partially extending a threaded pin assembly into one end of the parison; (c) partially closing the mold section about the pin assembly and parison; (d) further axially extending the pin assembly to insure sufficient amounts of plastic are worked into the threads of the pin; (e) completing the closure of the mold sections; and (f) expanding the parison into contact with the blow cavity of the mold sections. The Krall patent, therefore, contemplates compression molding of its internal threads by closing the mold sections around a rigid pin assembly; and utilizes axial movement of the pin assembly to sufficiently work the soft thermoplastic into the threads therein. After the forming procedure, the blow pin is unscrewed from the formed threads and the mold sections are separated.
Another method which contemplates the formation of internal attachment means in blow-molded articles is shown in U.S. Pat. No. 4,397,629, which issued to M. Akutsu et al. on Aug. 9, 1983. The Akutsu et al. process includes the steps of: (a) supporting an injection molded preform within a holding member; (b) inserting an expandable device into the mouth-neck portion of the premolded preform; (c) pushing a pressing rod axially upwardly within the expandable device thereby gradually expanding the device in the radial direction against the mouth-neck portion of the premolded article within a surrounding mold; (d) withdrawing the pressing rod, thereby allowing the expandable device to collapse to its original position; (e) removing the expandable device from the mouth-neck portion of the premolded article; and (f) subsequently utilizing conventional blow-molding techniques to form the balance of the premolded article into a bottle.
Other references have been directed to injection-molding articles having internal attachment means. For example, U.S. Pat. No. 3,247,548, which issued to M. R. Fields et al. on Apr. 26, 1966, shows a collapsible molding core which expands to form a part of a mold for injection-molding a closure cap having internal threads. In use, the collapsible core is expanded into molding position prior to introduction of molten plastic therearound. After the plastic has cooled sufficiently to retain its molded shape, the core is collapsed and retracted without inteference with the internal attachment means formed in the cap.
Despite all the prior work done in this area, there remain problems in efficiently blow-molding bottles having neck finishes with internal attachment means. With prior art methods, only inefficient, costly, and slow multi-step processes were available. Heretofore, a blow-molding process which could provide low cost and high quality bottles having neck finishes with internal attachment means was not known in the industry.